1. Field of the Invention
This invention relates to a sheet processing apparatus and an image forming apparatus provided with the same.
2. Description of the Related Art
Heretofore, some of image forming apparatuses such as a copying machine, a printer, a laser printer and a facsimile, and a compound apparatus of these have been designed such that an image forming apparatus main body is provided with a sheet processing apparatus for effecting such treatment as a stapling treatment on sheets discharged from the image forming apparatus main body.
As such a sheet processing apparatus, there is one designed such that sheets discharged from the image forming apparatus main body are conveyed to a sheet processing portion, and such treatments as a sheet stacking and aligning operation of stacking and aligning the discharged sheets, and a stapling operation of stapling the sheets are performed in the sheet processing portion.
Further, such a sheet processing apparatus is designed such that as shown, for example, in FIG. 1 of the accompanying drawings, after the treatments have been effected on the sheets, a sheet bundle is discharged from a treatment tray 602 to the inclined stack tray 601 of a main body external portion 600 by bundle discharging means 650, and in this case, the sheet bundle can be aligned in one direction from gravity by the inclination of the stack tray 601 (see Japanese Patent Application Laid-open No. 2002-284425).
As another sheet processing apparatus, there is known an apparatus designed such that sheets having images formed thereon are contained in stacking means, whereafter a sheet bundle is bundle-moved, whereafter such a treatment as a stapling treatment is effected on the sheet bundle, and thereafter the sheet bundle is again bundle-moved and contained in the stacking means (see Japanese Patent Application Laid-open No. H07-257811)
However, in such a conventional sheet processing apparatus and an image forming apparatus provided with the same, when the sheet bundle is to be stacked on the inclined stack tray 601, the sheet bundle can be aligned by the inclination of the stack tray 601, but when the sheet bundle is to be discharged to a substantially horizontal stack tray, the alignment of the sheet bundle by the gravity fall thereof cannot be effected. Therefore, depending on an inertial force or the condition of the sheet bundle, the position of the sheet bundle stacked on the stack tray after it has been discharged does not become constant, and the stacking property is reduced.
Particularly, in the case of an unstapled sheet bundle, the alignment in the sheet bundle is liable to deviate, and once it deviates, it is impossible to align the sheet bundle again. That is, in a case where the sheet bundle is discharged to the substantially horizontal stack tray, it has been difficult to stack the sheet bundle in its aligned state.
Also, when the treatment of the sheet bundle is to be effected in the afore described another conventional sheet processing apparatus, there is a case where sheets are discharged from a discharge path onto the treatment tray, so as to fly, and the discharged sheets are moved in a direction opposite to the discharging direction, and then the aligning operation is performed, whereafter the edge portions of the sheets in the conveying direction thereof are aligned, and then a sheet bundle is stapled (see Japanese Patent Application Laid-open No. 2002-37512).
In order to perform such an aligning operation, the sheet processing apparatus, as shown, for example, in FIG. 2 of the accompanying drawings, has a resilient member 671 called a paddle, and an aligning belt 619 rotated in synchronism with a discharge roller 617 for discharging a sheet S onto a treatment tray 672, and the trailing edge of the sheet S is pulled back to the nip point between the aligning belt 619 and the treatment tray 672 by the resilient member (paddle) 671, whereafter the sheet S is caused to abut against an alignment abutting member (not shown) by the frictional force of the aligning belt 619 to thereby regulate the position of the sheet in the conveying direction thereof and perform alignment.
Also, the sheet discharged onto the treatment tray and caused to abut against the alignment abutting member and having had its edge portion in the conveying direction aligned is thereafter subjected to such an aligning operation that it is nipped in its width direction by a width direction aligning member movable in the width direction orthogonal to the conveying direction, so that the position of the sheet in the width direction may be regulated.
Now, in the conventional sheet processing apparatus shown in FIG. 2 and an image forming apparatus provided with the same, to convey and align the sheets, several parts such as the discharge roller 617, the resilient member 671 and the aligning belt 619 are necessary, and this has led to a great number of parts including members around those parts.
Also, in a case where a frictional force obtained by the rotation of the resilient member 671 is utilized to effect the alignment of the sheets S in the conveying direction thereof, as the number of stacked sheets S increases, the amount of flexure of the resilient member 671 becomes greater, and along therewith, the contact pressure of the resilient member 671 with the sheet S increases, and when the sheet S abuts against the abutting portion, there has been the possibility of the sheet S being buckled. When in order to effect the alignment of the sheet S in the conveying direction thereof, a frictional force obtained by the rotation of the aligning belt is utilized as another means, there has been the possibility that deviation is caused to an aligned sheet bundle by the delicate vibration of the aligning belt occurring during the rotation of the aligning belt.
Further, the sheet S is discharged onto the treatment tray by the discharge roller 617 so as to fly and therefore, when the sheet S is discharged onto the treatment tray, the falling position of the sheet is not stable in some cases depending on the kind of the sheet S, and in such cases, it has sometimes been impossible to cause the discharged sheet to stably abut against the aligning and abutting portion.
Also, in a case where design is made such that the alignment of the sheet S in the width direction thereof is effected by a width direction aligning member, if a change occurs to the length of the sheet in the width direction thereof due to the influence of temperature, humidity or the like, the sheet may sometimes be buckled by this change in the length. On the supposition of such a change in the length of the sheet in the width direction thereof, it is also possible, for example, to adopt a construction in which a spring or the like is attached to the width direction aligning member to thereby enable the change in the length in the width direction to be absorbed to some extent, but the adoption of such a construction leads to a greater number of parts.
Further, in the conventional sheet processing apparatus, when the sheet is to be uniformized (aligned) in the width (a direction intersecting with the sheet conveying direction), as shown in FIG. 3 of the accompanying drawings, the sheet S conveyed to a treatment tray 800 in the direction indicated by the arrow A has been caused to abut against an abutting wall 803 with a width regulating plate 802 moved on the treatment tray 800 by a predetermined amount in the direction indicated by the arrow B orthogonal to the sheet conveying direction. The width regulating plate 802 is adapted to receive the driving force of a motor (not shown) through a rack and a pinion and be moved thereby. The width of the sheet being aligned also means that one side edge (hereinafter referred to as the side edge) Sa of the sheet S is aligned.
The amount of movement of the width regulating plate 802 is set to a distance of e.g. about 2 mm to about 3 mm further inwardly from a position at which the side edge Sa of the sheet S along the sheet conveying direction has abutted against the abutting wall 803. That is, the width regulating plate 802 is adapted to be moved to a position made narrower by about 2 mm to about 3 mm than the width size (a length C in FIG. 3) of each sheet.
However, in the conventional sheet processing apparatus provided with the width regulating plate 802, the amount of movement of the width regulating plate 802 is determined to about 2 mm to about 3 mm further from the position at which the side edge Sa of the sheet S has been caused to abut against the abutting wall 803, and this has led to the problem that in the case of an upper trough curl in which the opposite side edges of the sheet S face up, or a lower trough curl in which the opposite side edges of the sheet S face down, the width C of the sheet becomes narrower by the amount of curl of the sheet S than the actual width of the sheet, and the sheet cannot be caused to reliably abut against the abutting wall 803 by the predetermined width narrowing amount of the width regulating plate 802, and width aligning accuracy is remarkably lowered.
If the amount of movement of the width regulating plate 802 is made greater than about 2 mm to about 3 mm, when an uncurled normal sheet is pushed in, an overload is applied to a motor for moving the width regulating plate and the motor may lose synchronism. Therefore, the conventional sheet processing apparatus is designed such that the sheet is pushed in by the width regulating plate 802 by such a degree of distance (about 2 mm to about 3 mm) that the motor does not lose synchronism.
Also, when the sheet has come into contact with the width regulating plate 802, if the sheet is in an upper trough curled state, the sheet may more or less float up from the treatment tray 800 along the curl, and if conversely the sheet is in a lower trough curled state, the sheet may more or less float up from the treatment tray 800 in such a manner as to be turned up along the curl, and this has led to the problem that the width aligning accuracy is remarkably lowered.
Also, in the conventional sheet processing apparatus, the entire side edge of the sheet is pushed by the width regulating plate 802, and this has also led to the problem that if the size of the sheet during the cutting thereof is uneven, the width aligning accuracy cannot be enhanced.